High-energy x-ray imaging device and method therefor

ABSTRACT

The present invention relates to a high-energy X-ray imaging device that is suitable for precise medical diagnosis and capable of enhancing the accuracy of nondestructive examinations. The high-energy X-ray imaging device of the present invention comprises an electron-circulating type high luminance X-ray generator and a two-dimensional X-ray detector that is sensitized for high-energy X-rays. The electron-circulating type X-ray generating device consists of a tinytarget together with a LINAC or microtron injector and a synchrotron. The synchrotron stores electrons, and electrons are bombarded against a tinytarget placed on the electron orbit to generate high-energy X-rays. The means to sensitize the two-dimensional X-ray detectors consists of a thin film made of lead or other heavy elements. It is placed in front of and in close contact with the two-dimensional detector, such as X-ray film. The X-ray image thus generated is a transmissive image.

TECHNICAL FIELD

[0001] The present invention relates to a high-energy X-ray imagingdevice to be employed in industrial applications that use X-rays.Specifically, the present invention relates to a high-energy X-rayimaging device that is most suitable for radiography, X-ray therapy,nondestructive examinations, radioscopy, two-dimensional fluorescentX-ray analysis, topography, X-ray microscopy, and other X-ray relatedtechnologies.

BACKGROUND ART

[0002] Radiography uses approximately 60 keV X-rays. It has servedhumanity for the past 100 years, and has been increasingly popular inrecent years. The upper limit for X-rays used in nondestructiveexaminations is approximately 150 keV. Absorption contrast is used toimage objects in radiography and nondestructive examinations.High-energy X-rays have not been used in the past, except innondestructive examination of structures, because of their hightransmissivity. The spatial resolution of absorption images is limiteddue to the scattering of X-rays.

[0003] Medical exposure is one of the problems in radiography. X-rays ofabout 60 keV are significantly absorbed into the body so that severalrounds of exposure can easily exceed the legal limit. Both doctors andpatients are exposed to serious danger when an operation must be carriedout under X-ray visualization. Another problem is the accuracy of X-rayimages. It is difficult to identify a cancerous region of 1 mm or less.In a nondestructive examination, it is difficult to get sharp images dueto the scattering of X-rays. The absorption method, when high-energyX-rays or gamma rays are used, is not suitable for imaging lightelements, that is, living organisms and animate matter.

[0004] The objective of the present invention is to provide ahigh-energy X-ray imaging device that generates high luminance andhigh-energy X-rays using an electron-circulating type X-ray generatingdevice.

[0005] It uses high-energy X-rays of 100 keV to several tens of MeV thathave never been used before, and the device images transmittable X-rayimages of high accuracy aided by a two-dimensional X-ray detector inwhich its detection sensitivity is increased by the use of a thin filmmade of lead or other heavy elements. The high-energy X-ray imagingdevice also produces very fine images of both structures andbio-substances made up of light elements using the effect of refractioninterference arising from the phase shift of X-rays due to density.

DISCLOSURE OF INVENTION

[0006] The technical resolution means adopted by the present inventionis: A high-energy X-ray imaging device comprising an X-ray generatingdevice that uses relativistic electrons and a two-dimensional X-raydetector, wherein said X-ray generating device generates high-energyX-rays, and said two-dimensional X-ray detector detects high-energyX-rays that pass through the body being tested.

[0007] Said high-energy X-ray imaging device may include, as said X-raygenerating device, tinytarget together with a LINAC, microtron,betatron, or electron-circulating type X-ray generating device usingsynchrotron, or electron-storage ring.

[0008] Said high-energy X-ray imaging device may include said X-raygenerating device in which the electron energy is controlled at 8 MeV orbelow.

[0009] Said high-energy X-ray imaging device may use, as saidtwo-dimensional X-ray detector, at least one X-ray film, nuclear dryplate, imaging plate, X-ray tube or CCD camera for imaging.

[0010] Said high-energy X-ray imaging device may be provided, upstreamof said two-dimensional X-ray detector, a thin plate made of lead,tungsten, gold, platinum, silver, tin, antimony or other heavy elementsfor the purpose of enhancing the efficiency of high-energy X-raydetection.

[0011] To enhance the efficiency of detection by said two-dimensionalX-ray detector, said high-energy X-ray imaging device may be provided,downstream of said thin plate, a fluorescent plate in close contact withsaid two-dimensional X-ray detector, or fluorescent substances may becoated or deposited on the thin plate on the surface facing saidtwo-dimensional detector, or the fluorescent substances may be coated ordeposited on the detecting surface of said two-dimensional X-raydetector.

[0012] Said high-energy X-ray imaging device may also include, upstreamof the body being tested, a low-energy X-ray absorbent for the purposeof reducing low-energy X-ray exposure and enhancing the resolution ofX-ray images.

[0013] Said high-energy X-ray imaging device may use, as the low-energyX-ray absorbent, a plate made of beryllium, polymer membrane, graphite,aluminum, silicon, iron, copper, nickel or other light elements.

[0014] It is another objective of the present invention to provide ahigh-energy X-ray imaging method wherein high-energy X-rays, generatedby an X-ray generating device using relativistic electrons, areirradiated onto the target and the transmissive X-rays are imaged astwo-dimensional images.

BRIEF DESCRIPTION OF DRAWINGS

[0015]FIG. 1 is a general plan view illustrating the high-energy X-rayimaging device of the present invention;

[0016]FIG. 2 is a photograph of a swallowtail butterfly photographed bythe high-energy X-ray imaging device;

[0017]FIG. 3A is a stainless steel nut; and

[0018]FIG. 3B is a 1 mm thick aluminum mesh, both photographed by thehigh-energy X-ray imaging device of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] The high-energy X-ray imaging device of the present invention isdescribed in detail using FIG. 1. FIG. 1 is a general plan view of thedevice. The high-energy X-ray imaging device of the present inventionincorporates the electron-circulating type X-ray generating device 1 asa means of generating X-rays using relativistic electrons. X-rayluminance of the electron-circulating type X-ray generating device,which has a very small source point thus the device is suitable for thehigh-energy X-ray imaging device of the present invention. It ispossible to generate X-rays by irradiating relativistic electronsgenerated by a LINAC, microtron, betatron or synchrotron onto thetinytarget or by placing the tinytarget on the orbit of the relativisticelectrons generated by the LINAC, microtron, betatron or synchrotron.The electron-circulating type X-ray generating device shown in FIG. 1 isa known type. It consists of a vacuum tank 1A, electron-storing ring 2,incident port 1B guiding electrons into the vacuum tank 1A, Q magnet 1C,klystron 1D, electron gun 1E, vacuum pump 1F, beam line 1G, andmicrotron injector 3. High luminance X-rays are generated by placing atarget on the electron orbit of the electron-storing ring 2 and bystoring electrons. In this FIG. 1, the electron beam injector is a smallmicrotron 3. The electron energy of the microtron is 6 MeV. This levelof energy is adopted because nuclear reaction does not occur when theelectron energy is below 8 MeV. Accordingly, the device of the presentinvention does not generate neutrons thus lead and iron are used toshield radiation; concrete shields are not necessary. Electrons of 6 MeVenter and are stored on the electron-storing ring 2 and a tiny solidtarget 4 is placed on the electron orbit to generate X-rays. The targetis a thin wire of tungsten, gold, lead, etc. several microns to severalmillimeters in diameter, and a thin film may also be used as well as Siand other crystals.

[0020] X-ray beam 12 is extracted through the beam line 6 shown inFIG. 1. The spread of the X-ray beam 12 is approximately 0.08 rad.Accordingly, the size of the window of the beam line 6 is approximately10 cm in diameter. The vacuum window of the beam line 6 is made ofapproximately 1 mm thick aluminum to absorb low-energy X-rays. That is,the beam line 6 has another function that is reducing low-energy X-rayexposure. It is recommended that the thickness be varied according tothe application. This particular X-ray generating device emits softX-rays also. To facilitate replacement of low-energy absorbents, apolymer thin film of beryllium, plastics, etc., or approximately 0.1 mmthick aluminum is used as the window material, and X-ray absorbents areplaced separately. The X-ray absorbent is optimized by varying thethickness of the beryllium, polymer film or aluminum. Various thin filmscan be used such as gold, lead or tin. However, use of lead, gold andother heavy elements will generate fluorescent X-rays, and these becomea new source of X-ray emissions resulting in increased imaging defects.Use of heavy metals is therefore not recommended.

[0021] The two-dimensional X-ray detector 7 shown in FIG. 1 is describedbelow.

[0022] The two-dimensional X-ray detector 7 detects X-rays that passthrough the body being tested. It has the same structure as an X-raydetector of a known X-ray inspection system. The detector is placedfacing the above-mentioned-beam line 6. As the detector 7, an X-rayfilm, nuclear dry plate, CCD camera for X-rays, X-ray tube, imagingplate or other commercially available part is used. In FIG. 1, an X-rayfilm is used as the X-ray detector 7. To enhance the efficiency of X-raydetection in the present invention, a (thin) lead plate 9, severalmicrons to several mm thick, is placed in front of and in close contactwith these X-ray detectors 7. The thin lead plate 9 is used to vary thewavelength of the X-rays. A 0.1 mm thick lead plate 9 is used in thisparticular example. The X-ray spectrum of the electron-circulating typeX-ray generating device ranges from several keV to 6 MeV. High-energyX-rays of 80 keV and above are absorbed due to the photoelectric effectof the lead and emitted again as low-energy fluorescent X-rays, whichare detected by the X-ray film 7. Within the lead material, thehigh-energy X-rays generate electrons by Compton scattering. X-ray film7 is highly sensitive to these electrons and the electrons thusgenerated also generate bremsstrahlung, further increasing thelow-energy X-rays.

[0023] Furthermore, electron pairs are generated when X-rays of 1.1 MeVand above enter the lead material. The X-ray film 7 is also highlysensitive to the electrons and positrons generated in this way. Thewavelength varying materials are not limited to lead. Since heavyelements have a high conversion efficiency, tungsten, gold, platinum,silver, tin and antimony are all good materials for the thin plate 9,though the conversion efficiency is lower than that of lead.

[0024] Another advantage of placing a thin lead film 9 in front of theX-ray film 7 is to cut off X-rays of 80 kV and below. X-ray linearity isproportional to the energy level. Low-energy X-rays are easilyscattered. The scattered X-rays at the specimen or the body being tested11 and beam line 6 are the cause of blurred X-ray images. Thin leadplates are an effective means of eliminating this cause.

[0025] The use of fluorescent plate 10 is described below. This platemay or may not be used. Fluorescent plates have a sensitizing effect,that is, a fluorescent plate converts X-rays to visible light, therebyenhancing the film's sensitivity. The problem is that the derived imageis blurred depending on the thickness of the fluorescent plate. To avoidthis problem, fluorescent substances are directly coated or deposited onthe thin lead plate 9 on the surface facing the two-dimensional X-raydetector 7. It is also possible to coat the fluorescent substancesdirectly on the surface of the detector 7. It is also good to usenuclear dry plates as high-energy X-ray film.

[0026] X-ray photographs derived from the high-energy X-ray imagingdevice of the present invention are shown in the attached figures. Thesolid target 4 is a 0.5 mm tungsten wire. The vacuum window is made of 1mm thick aluminum. The sensitizing material used is a 0.2 mm thin leadfilm. The X-ray film used is an ordinary direct radiographic film. Thespecimen and the film are in direct contact with each other in theseexamples. Even when they are separated by 1 meter, an image of the samecontrast can be obtained except that the size is approximately doubled.FIG. 2 is an image of a swallowtail butterfly. No fluorescent plate wasused for this image. The image clearly shows the structure constructedby light elements such as the body, skeleton, interior of the eyes,tactile organ, straw, gussets on the abdomen and the profiles ofparticulate matter. It is not definitely known why a butterfly made oflight elements can be so sharply imaged with high-energy X-rays, butthis is probably because of interference of the X-rays. X-rays willshift phase according to the difference of density and they arerefracted. At the boundaries where different densities meet, refractedX-rays interfere with non-refracted X-rays and generate light-and-darkinterference patterns. Phase shifting of X-rays greatly depends on thedensity of the substances photographed. Interference occurs at theboundaries of substances of different densities and depict the boundarysharply. For example, cancer cells and healthy cells have a similarelement structure but have different densities. This is the reason whythe high-energy X-ray imaging device of the present invention can easilyidentify cancer cells.

[0027]FIG. 3A is a steel nut. This and the next sample were imaged usinga fluorescent plate. The 4 mm thick stainless steel nut was imaged bytransmission just as though we were looking at a pane of glass. Onlyhigh-energy X-rays produce X-ray images like this. The top and bottomsurfaces of the nut are also clearly imaged. FIG. 3 is a 1 mm mesh madeof 1 mm thick aluminum. This is also a transmission image.Light-and-dark contrast occurs around the openings of the mesh, showingthat this is also an interference image.

[0028] The above description shows that the high-energy X-ray imagingdevice of the present invention provides transmission X-ray images ofvery high precision, and is suitable for imaging both light and heavyelements. The device exhibits excellent performance in both medicaldiagnosis and nondestructive examinations. Furthermore, sincehigh-energy X-rays have high transmissivity and are hardly absorbed inthe human body, the device of the present invention significantlyreduces exposure to radiation.

[0029] The present invention may be implemented in any other form ofembodiment without deviating from the spirit of the main featuresthereof. The above-mentioned embodiments are therefore only a fewexamples and should not be construed as limiting.

[0030] Industrial Applicability

[0031] As detailed above, the high-energy X-ray imaging device of thepresent invention generates high luminance high-energy X-rays using itselectron-circulating type X-ray generating device. It uses high-energyX-rays of 100 keV to several tens of MeV that have not been used inconventional devices. The detection sensitivity of the two-dimensionalX-ray detector is enhanced by using thin films made of lead and otherheavy elements to aid in the generation of transmissive high-precisionX-ray images. The high-energy X-ray imaging device of the presentinvention uses the phenomenon in which the phase of the X-rays isshifted by density and triggers refraction interference, and thereforeis sensitive to the boundaries of substances. For this reason thehigh-energy X-ray imaging device of the present invention generatesprecise images for not only bio-substances made of light elements butalso structures. For example, the device identifies cancer cells andhealthy cells because they have different densities. It is also possibleto identify types of cancers by noting differences in shape. High-energyX-rays have high transmissivity, and as a result, the device offers theremarkable effect of reducing exposure to radiation in medicalapplications.

What is claimed is:
 1. A high-energy X-ray imaging device comprising: anX-ray generating device that uses relativistic electrons; and atwo-dimensional X-ray detector, wherein said X-ray generating devicegenerates high-energy X-rays and said two-dimensional X-ray detectordetects high-energy X-rays that pass through a body being tested.
 2. Thehigh-energy X-ray imaging device as claimed in claim 1 wherein saidX-ray generating device is a LINAC, microtron, betatron orelectron-circulating type X-ray generator using synchrotron or electronstorage ring.
 3. The high-energy X-ray imaging device as claimed inclaim 1 or 2, wherein electron energy of the high-energy X-rays isgenerated in the X-ray generating device is 8 MeV or below.
 4. Thehigh-energy X-ray imaging device as claimed in any of claims 1 through3, wherein one of an X-ray film, nuclear dry plate, imaging plate, X-raytube and CCD camera for imaging is used as said two-dimensional X-raydetector.
 5. The high-energy X-ray imaging device as claimed in claim 4,wherein a thin plate made of lead, tungsten, gold, platinum, silver,tin, antimony or other heavy elements is placed upstream of saidtwo-dimensional X-ray detector to enhance the efficiency of high-energyX-ray detection.
 6. The high-energy X-ray imaging device as claimed inclaim 5, wherein a fluorescent plate is placed downstream of said thinplate in close contact with said two-dimensional X-ray detector, orfluorescent substances are coated or deposited on said thin plate on asurface facing said two-dimensional detector, or the fluorescentsubstances are coated or deposited on a detecting surface of saidtwo-dimensional X-ray detector to enhance efficiency of X-ray detectionby said two-dimensional X-ray detector.
 7. The high-energy X-ray imagingdevice as claimed in any of claims 1 through 6, wherein a low-energyX-ray absorbent is placed upstream of the body being tested for thepurpose of reducing low-energy X-ray exposure and enhancing theresolution of X-ray images.
 8. The high-energy X-ray imaging device asclaimed in claim 7, wherein said low-energy X-ray absorbent is a platemade of beryllium, polymer membrane, graphite, aluminum, silicon, iron,copper, nickel or other light elements.
 9. A high-energy X-ray imagingmethod, wherein the high-energy X-rays generated by a X-ray generatingdevice using relativistic electrons are irradiated onto an object andthe transmitted X-rays are captured to generate two-dimensional images.